Aerospace systems, as well as components for gas turbine and rocket engines, routinely require high temperature surface stability during service. Commercially available nickel-based superalloys with controlled microstructures, which rely on the formation of a continuous and adherent thermally grown oxide (TGO) scale of α-Al2O3 for extended resistance to degradation, may be used for high-strength thermal protection components. However, most commercial Ni-based superalloys were developed more for high-temperature strength than for oxidation resistance.
U.S. Pat. No. 7,273,662, incorporated herein by reference, describes alloy compositions and coatings including a Pt-group metal, Al, a reactive element such as Hf, and Ni, which have a predominately γ′-Ni3Al+γ-Ni phase constitution. These alloy compositions are sufficiently low in Al content to be substantially free of β-NiAl, and form metallic coatings with improved reliability and durability. Further, these alloy compositions form highly adherent, slow-growing TGO scales during both isothermal and cyclic oxidation at high temperatures.